Among various known sailboats, a sailboat having a propulsion device, such as a stern drive, can travel in two ways: under sail using the force of wind received by a sail without operating the engine; or under power using the propulsion force of a propeller with the engine operated.
A typical sailboat propulsion device has a drive unit incorporating a clutch, a gear, a bearing and the like for transmitting the engine drive power to a propeller shaft. Even when traveling under sail with the engine not operating, the propeller rotates due to water resistance. The sailboat could go even faster when traveling under sail than under power. Therefore, in order to prevent the seizure of a clutch, gear, bearing etc., it is necessary to provide lubricating oil to sliding parts of a driveline not only when traveling under power but also when traveling under sail with the engine stopped.
In view of this objective, a saildrive system having a centrifugal pump integrated into a propeller shaft, or into a drive shaft that connects a propeller shaft and a clutch with a bevel gear, has been suggested. In this system, when the boat travels under power, lubricating oil is absorbed by the centrifugal pump from an oil reservoir in the bottom of the casing, and the pressurized oil is circulated in a lubricating oil path formed inside the casing for supply to the clutch, gear, bearing etc. This system is disclosed, for example, in Japanese Unexamined Patent Publication No. H03-7691, Japanese Unexamined Patent Publication No. H06-331838, and Japanese Unexamined Patent Publication No. 2000-318688.
Also, Japanese Unexamined Patent Publication No. H04-143195 discloses a structure in which a wet multiplate forward and reverse clutch is integrated into a drive unit of a propulsion device, and an input shaft to which engine drive power is applied is directly connected to a gear pump, which supplies lubricating oil or working oil for the clutch.
This gear pump directly connected to the input shaft is not capable of supplying lubricating oil when the engine is stopped; that is, lubricating oil is not supplied when the boat travels under sail with the engine not operating. Meanwhile, the centrifugal pump integrated into the propeller shaft or drive shaft does not work without the rotation of the propeller shaft or drive shaft. Therefore, working oil is not supplied to the hydraulic wet multiplate clutch when the boat is stopped, and the clutch cannot be engaged. In view of this defect, the existing sailboat having a centrifugal pump driven by the propeller shaft or drive shaft generally uses a cone clutch operated by a mechanical shift mechanism, instead of a hydraulic wet multiplate clutch.
However, compared with a hydraulic wet multiplate clutch, the cone clutch generates a large impact when switching between forward and reverse. Particularly, for certain types of sailboats in which it is desirable to increase the cabin area that lies adjacent to the engine room, and in which comfort is important, the engine room needs to be reduced in size to enlarge the cabin area. However, a smaller engine room more easily transmits noise to the cabin area, which can be significantly bothersome.
In view of this problem, an object of the present invention is to provide a hydraulic saildrive apparatus having a hydraulic wet multiplate clutch.